Post-traumatic or post-operative immobilization of cervical spine often requires long term bed-rest. But, bed-rest indeed gave discomfort to patients, nonetheless, sometimes complete external fixation cannot be gained. Since 1982, we have applied Halo vest to the patients who required external immobilization of cervical spine. In this paper, we reported our experiences with 31 cases who were treated by Halo vest. Thirty-one cases comprised 19 cases of cervical spinal trauma, 5 cases of atlanto-axial dislocation, 1 case of foramen magnum meningioma, and 6 cases of ossification of posterior longitudinal ligament (OPLL). In traumatic cases, Halo vest was used as external fixation of injured spine in 8 cases, and as an adjunct to surgical fusion in other cases. In case of atlanto-axial dislocation, 3 cases underwent posterior fusion, and 2 cases underwent anterior fusion. Anterior fusion of C1-2 was also done in case of foramen magnum meningioma after total excision of tumor. Six cases of OPLL underwent anterior decompression and anterior fusion. Mean immobilization time by Halo vest was as follows: 58 days (28-113) in case of cervical spinal trauma, 85 days (56-144) in case of atlanto-axial dislocation who underwent posterior fusion, 92 days (89-93) in case of atlanto-axial dislocation and foramen magnum meningioma who underwent anterior fusion, 59 days (54-70) in case of OPLL. Early ambulation was achieved in many cases. Good external fixation and result was obtained 27 cases out of 31 cases. Re-dislocation of cervical spine occurred in 1 case of cervical spinal trauma while he was in Halo vest.(ABSTRACT TRUNCATED AT 250 WORDS)